An underground tank holding some of the worst radioactive waste at the Hanford Nuclear Reservation might be leaking into the soil.

The U.S. Energy Department has been actively monitoring double-shell tank AY-102 since it was discovered to have a slow leak from the primary tank. Yesterday, workers detected an increased level of contamination during a routine removal of water and survey of the leak detection, which are routinely pumped to remove water and sediment. Then the pumps are surveyed for any radiological contamination.

The source of the contamination is not yet verified, but may be an indication of a leak from AY-102 tank's secondary containment.

Spokeswoman Lori Gamache says further assessment must be completed before a determination can be made regarding the contamination source.

Office of River Protection has notified the Washington State Department of Ecology and U.S. Environmental Protection Agency, and convened an engineering analysis team to conduct additional sampling and video inspection to further assess the elevated radiation levels and determine the source of contamination.

AY-102 is one of Hanford's tanks with two walls, which were installed years ago when single-shell tanks began leaking.

Some of the worst liquid in those tanks was pumped into the sturdier double-shell tanks.

The tanks are now beyond their intended life span. The Energy Department announced last year that AY-102 was leaking between its two walls, but it said then that no waste had escaped.

“This is most disturbing news for Washington. It is not clear yet whether that contamination is coming directly from the outer shell of the AY-102 but it must be treated with the utmost seriousness.... Our state experts confirm that there is no immediate public health threat. Given the relatively early detection of this potential leak, the river is not at immediate risk of contamination should it be determined that a leak has occurred outside the tank. The Secretary [Moniz] assured me that USDOE will respond swiftly and with all actions necessary to determine the condition of the AY-102... We will be insisting on an acceleration of remediation of all the tanks, not just AY-102. USDOE has a legal obligation to clean up Hanford and remove or treat that waste, and we ensure that legal obligation is fulfilled.”